1. FIELD OF INVENTION
This invention generally relates to a vacuum-operated brake booster, and more particularly to a retainer for a key which limits the retraction travel of a power piston and a valve mechanism.
2. DESCRIPTION OF THE PRIOR ART
A vacuum-operated brake booster having a key which limits the retraction travel of a power piston and a valve mechanism by contacting a housing is disclosed in U.S. Pat. No. 4,587,885. The key of this vacuum-operated brake booster is provided with a pair of legs inserted into a radial hole of the power piston. A valve plunger is slidable axially in response to movement of a push rod coupled with a brake pedal. The legs are inserted into a circular center groove of the valve plunger so as to straddle and press against the valve plunger. The key is further provided with a retainer arm portion which engages an outer circumferential surface.
The key is prevented from radially falling out of the hole by an engagement between the ends of the legs and a rib formed in the radial hole of the power piston. This engagement is accomplished by effecting a plastic deformation of the legs by means of a tool.
The above prior art vacuum-operated brake booster, however, presents a manufacturing drawback due to the manner of retaining the key in the hole. That is, when deforming the legs by the tool, the power piston, formed of a resin, may be damaged.